Question for BoKu

Discussion in 'Composites' started by RSD, Oct 14, 2019.

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  1. Oct 26, 2019 #21

    Lendo

    Lendo

    Lendo

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    RSD, Colan is a well know manufacturer and supplier in Australia.
    George
     
  2. Nov 7, 2019 #22

    Scheny

    Scheny

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    As for the red fabric, be careful! I have used this for my boat (in black/blue) and it is super cheap colored glass and definitely not Kevlar! Do not use it in structural applications.

    It is sold in Europe as design-sheets and also the black is colored glass. It is available in blue, green, red, black and even silver (real aluminized). There are versions with real glass, but they are at least 4 times as expensive...

    BR, Andreas
     
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  3. Nov 7, 2019 #23

    BoKu

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    Easy enough to test for--just burn some. Glass doesn't burn, and aramids burn with a distinctive odor.
     
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  4. Dec 4, 2019 #24

    Scheny

    Scheny

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    As the thread is already called question for BoKu, I didn't want to open another another thread with the same name.

    In the Raptor I got from the video that the fuselage is made from around 40oz or 1500g carbon with 1/2 inch core only in selected areas.

    I seem to recall your HP-24 also has a fuselage without sandwich, so as also a lot of other gliders. I would like to know out of interest what thickness is generally used there?

    From my smallest boat I know that there a sandwich of 2x6oz 2mm foam then 2x6oz again is substituted by 2x6oz, 3x12oz,2x6oz of glass for solid layups, doubling the weight in total.

    Even kayaks only do this for white water, otherwise they switch to at least Soric if not Airex. So why in aerospace?
     
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  5. Dec 4, 2019 #25

    BoKu

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    I originally designed the HP-24 fuselage to be made of fiberglass, with a base layup of 5 plies of 7725, three at 0/90 and two +/-45. That was what George Applebay recommended. When we switched to carbon, I decided to simplify the layup at the expense of weight. Now we just use three plies of 11oz carbon, first and last at 0/90 and the middle one at +/-45. Plus reinforcements at the wing side of body and cockpit rail. The total thickness and fiber distribution is similar to what the Europeans are doing. After the shell cures, we add five or six ring stiffeners inside the aft fuselage, and the kit builder installs a bunch of bulkheads and longerons in the mid and forward fuselage areas. The only core foam is in the vertical fin; we put it down under the last 0/90 ply. The primary optimization here is getting a 22-foot long thing with 42 square feet of area laid up and bagged inside of two hours using relatively unskilled labor.
     
  6. Dec 4, 2019 #26

    Scheny

    Scheny

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    Thanks for the reply BoKu! So you alo have roughly the 1500g as with the kayak layup. I was just wondering why not using Coremat (hand layup version of Soric), as this saves 40% of weight. Does a glider need the weight for good L/D?

    BR, Andreas
     
  7. Dec 4, 2019 #27

    BoKu

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    I don't understand. How does adding material save weight?

    Our layup is primarily driven by requirements for torsional and bending stiffness in the aft fuselage. We use the same layup nose to tail for simplicity. There are few if any places where Soric or its kin would add anything of value, certainly not in proportion to the added complexity during the layup.
     
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  8. Dec 5, 2019 #28

    Lendo

    Lendo

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    Scheny,
    Without going into the Maths. a basic explanation for the Layman is, Core thickness adds stiffness, the thicker the core the stiffer the end result of what ever your making. I've noticed 1/2" Core used for stiffness to hold a shape in construction where 1/4" would be strong enough. Also Carbon is much stiffer than Glass and 'Rule of Thumb' you can use 50% weight Carbon to that recommended as E-Glass (Carbon 40% lighter with 60% more strength). As well the reduction of Resin needed in the Carbon adds to weight savings. S -Glass is a similar strength to Carbon, but Carbon has the stiffness and weight advantage. For example where you might use 3 layers of E-glass, with Carbon you could use 2 layers and a thinner Core, you can start to see the weight savings developing, alas costs also go up with Carbon.
    Do your research and see what's best for you, just remember Carbon fails catastrophically.
    I think you will find in the Spruce Catalog a Carbon weight, which would be a replacement for the 7725 E-glass - from memory.
    I'm in Australia so the local material is a little heavier, so check it for yourself.
    George
     
  9. Dec 5, 2019 #29

    BoKu

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    Just so, when it comes to panel stiffness against out-of-plane loads. And, of course, that panel stiffness helps resist crippling failures such as where the wall of a tube buckles when a bending moment is applied to it, so a sandwich tube might have more ultimate bending strength than a non-sandwich tube.

    What core thickness doesn't do is increase the overall bending or torsional stiffness of the tube. And quite often, it's that kind of stiffness that bounds its utility, especially where flutter is concerned.
     
    Last edited: Dec 5, 2019
  10. Dec 6, 2019 #30

    Lendo

    Lendo

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    Scheny, One of my concerns with Core material isn't always mentioned is compression strength. I like the compression strength of Last-A Foam (LAF) for it's weight, I also like it's sand-ability, but because of it's crumbly nature my concern is the adhesion strength to surface skins. In Composites it's the Core that transfers loads from one skin to another, if a skin separates from the core because of poor adhesion, there can be a failure. What I like about Divinycell (DC)and other more expensive foam cores, is their adhesive qualities, BUT their compression strength indicated by their Density, has be sufficient, not only on transferring loads but in Impact resistance. It is well known in engineering that failure of a substrate takes the surface material with it, no matter how good, how strong, the surface material will fail if it's supporting substrate fails.
    Now the only way to test these materials is to get samples and test them against LAF, just squeeze them between thumb and forefinger will give you the results you need.
    You will find a low density DC streets ahead in strength compared to LAF, but not the compression strength.
    Just my opinion from a lot of different foam testing, bottom line I wouldn't just go spec sheets alone when selecting any sort of core material.
     
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